The invention relates generally to double-faced display devices, and more particularly to a kind of double-faced light emitting diode display.
Today, flat panel technologies are in widespread use in computers, mobile communications, consume electrical products, and so on. Light emitting diodes have generally been recognized as good light sources for flat panel displays for a number of reasons. These include their solid state operation, their capability to be made relatively small (thus potentially increasing resolution), and their potential for yielding relatively low manufacturing costs. A flat panel display adopting light emitting diodes is called a light emitting diode display.
FIGS. 6 and 7 represent a conventional light emitting diode display disclosed in China patent no. 96199365.0. The light emitting diode display 10 includes a printed circuit board (PCB) 12, a shield panel 13, and a bracket 16. A plurality of pixel units 11 are formed on a surface (not labeled) of the PCB 12 that faces the shield panel 13, and a circuit driving system 19 is formed on an opposite surface (not labeled) of the PCB 12 that faces the bracket 16. The PCB 12, the shield panel 13 and the circuit driving system 19 are fixed into a whole unit by a pin 17. The circuit driving system 19 includes a row driver and a column driver. Each pixel unit 11 includes three light emitting diodes having three optical primary colors (i.e., R (red), G (green) and B (blue) respectively), a common anode electrically connected with each of the three light emitting diodes, and three cathodes electrically connected with the three light emitting diodes respectively. The row driver is connected with the common anode to drive the common anode to switch the circuit of the pixel unit on or off, and the column driver is connected with the cathodes to drive the cathodes to control the brightnesses of the light emitting diodes, whereby a color displayed by the pixel unit is controlled.
When a video signal is input to the light emitting diode display 10, the row driver drives the common anodes of the relevant pixel units 11 to switch the circuits of the relevant pixel units 11 on according to the video signal. Simultaneously, the column driver drives the cathodes of the relevant pixel units 11 to control the brightnesses of the light emitting diodes according to the video signal. In this way, colors displayed by the relevant pixel units 11 are controlled according to the video signal. Thus, a video image according to the video signal is displayed on the shield panel 13.
In the light emitting diode display 10, only a single image is displayed on the shield panel 13. However, in certain applications, simultaneously displaying of images at two opposite sides of the light emitting diode display 10 is required. In order to meet such needs, China patent no. 02123762.X discloses a double-faced light emitting diode display. As shown in FIG. 7, the double-faced light emitting diode display includes an enclosure, and a light emitting module packed in the enclosure. The enclosure includes a front portion 1, a front transparent protecting film 8, a back portion 2, and a back transparent protecting film 3. The light emitting module includes a light guide plate 6, a pair of astigmatism layers 9, 4 formed on opposite surfaces of the light guide plate 6, and a pair of light emitting diodes 7 located at opposite side extremities of the light guide plate 6.
In use, the light emitting diodes 7 emit light having a single color, and the colored light passes through the light guide plate 6 and the astigmatism layers 9, 4. Thus, a pair of colored signs can be displayed on the transparent protecting films 8, 3 respectively.
However, the double-faced light emitting diode display can only display simple signs having a single color. Such display can be used in traffic signal boards and certain limited applications only, and cannot be used for applications requiring large-scale full color displays.
What is needed, therefore, is a double-faced light emitting diode display having full color display capability. Desirably, the double-faced light emitting diode display would also have a simple structure, small bulk, and low cost.